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This letter presents an ultralow noise K-band low-noise amplifier (LNA) using substrate integrated suspended line (SISL) technology. A simplified, purely distributed parameter matching network is utilized for simultaneous noise and impedance matching. Different from standard chip-level circuits, a K-band LNA based on board-level platform with low-cost FR4 is proposed. Using the high-Q value of the SISL platform, this LNA shows the advantages of high-power gain, ultralow noise, and self-packaging. According to the measurement, the proposed LNA achieves a 27.7-dB small signal gain with 2.4-GHz 3-dB bandwidth (25-27.4 GHz) and noise figure (NF) of 1.0 dB with 20-mW power dissipation.

A radio frequency memory (RFM) based on microwave photonic mixing and digital RFM is proposed and demonstrated. By introducing the microwave photonic mixing, the operational frequency range is largely extended. Besides, the mixing spurs are effectively suppressed, which is important to guarantee the system efficiency and avoid generating significant feature for the jamming recognition. Meanwhile, by applying the digital RFM, flexible modulation and reconstruction are achieved. A proof-of-concept experiment is carried out. The wide working frequency range from C- to Ka- bands is achieved. The mixing spurs over the 0-40 GHz frequency range are experimentally suppressed. Radar imaging is successfully deceived. A radar waveform with a bandwidth of 500 MHz in the K band is successfully received and reconstructed. Two false targets are added. To the best of our knowledge, it is the first time that a photonics-assisted RFM is reported to have the functions of storage, flexible modulation, and reconstruction with wideband RF signals at a high frequency. The proposed scheme shows the great potential to be applied in electronic warfare, electronic environment simulation and testing, and so on.

The grains of oriented W-type hexaferrite BaNi2GdxFe16-xO27 (BaW) where x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 grew uniformly along their c-axis perpendicular to the sample plane, which meant high remanence ratio of BaW. When Gd3+ substitution content was x = 0.0, the corresponding remanence ratio reached as high as 0.90. When x = 0.2, the oriented BaW simultaneously possessed high saturation magnetization (Ms= 58.36 emu/g), high coercivity (Hc = 1527 Oe), high remanence ratio (Mr/Ms = 0.85), relatively low magnetocrystalline anisotropy field (Ha = 10,253 Oe) and low ferromagnetic resonance linewidth (ΔH = 624 Oe). These characteristics indicated the material was suitable for the design of self-biased circulator operated at K band. Based on the BaW material, self-biased double Y-junction microstrip circulator was designed and realized well circulatory function at K band.

Low cost, miniaturization, and high gain are the most essential prerequisites for multiband antennas (MBA). Therefore, a tactical effort is made in this paper to realize a small-size MBA (X, Ku, K-...

The hybrid integration of an additively fabricated air-filled waveguide (WG) with a printed circuit board (PCB) is presented. An arrangement is proposed where different waveguiding structures share the same common metal plane on PCB. Such an approach allows combining the low-loss and high- $Q$ properties of an air-filled waveguide, active circuit realization of the strip transmission line, and 3-D capabilities of additive manufacturing. A broadband transition is developed employing a through-patch coupling interface from a microstrip (MS) line to a waveguide. The concept was experimentally validated with exemplary transitions operating within $X$ -band and $K$ -band, featuring a measured bandwidth of $f_{h}/f_{l}~ \approx ~1.4$ and average per-transition loss including connecting lines of ~1.2 and ~1.9 dB, respectively.

A planar dual-band shared-aperture array antenna for the ${K}$ -/ Ka -band low Earth orbit (LEO) satellite communication is presented in this article. Substrate integrated coaxial line (SICL)-fed bow-tie transverse slots and substrate integrated waveguide (SIW)-fed slot pairs are employed to provide ${K}$ -band horizontal polarization and Ka -band vertical polarization, respectively. The ${K}$ -band and Ka -band radiating elements share a common metallic-via-array, which can effectively improve the port-to-port isolation. Furthermore, the port-to-port isolations in both bands can be also improved by introducing the high-pass characteristic of SIW and out-of-phase cancellation between two current paths. For the sake of achieving low-profile height and compact size, the ${K}$ -band feeding network is subtly buried between Ka -band shielding cavities. As a proof-of-concept example, a shared-aperture dual-polarized array antenna operating at ${K}$ -/ Ka -band is designed and fabricated for verification by using a multilayer printed circuit board (PCB) technology. The measured results show a good concordance with the simulated one, indicating that the proposed antenna has the advantages of wideband, high isolations, low profile, and easy planar integration, which can be adopted for the millimeter-wave (mm-Wave) LEO satellite communication system.

An efficient multifunctional metasurface for cross and circular polarization conversion is presented in this letter. The metasurface acts not only as an efficient polarization converter for linearly polarized wave over frequency bands of 5.3–5.4, 7.2–8, and 12.3–13.76 GHz but also perfectly converts linearly polarized wave into circularly polarized wave over multiple bands of 5.1–5.2, 5.6–6.85, 8.8–11.2, and 14.9–20.2 GHz. The behavior of the metasurface is quite stable under oblique incidence for certain bands up to 75°. The broadband circular- polarization conversion, compactness, angular stability, and multiple functionality make it a strong candidate for many applications in the strategic C -, X -, Ku -, and K -bands.

Active millimeter-wave (mmWave) imaging illuminates a scene with a source of mmWave energy and forms images based on the reflected energy. When imaging objects (such as packaged goods in commerce) that have a mixture of opaque and translucent parts, two-sided reflection imaging can be used to overcome the occlusion by the opaque objects that would plague a transmission imaging approach. However, the two-sided reflection imaging approach suffers from wavelength-dependent beat patterns when coherently combining the images from each side. We present and experimentally verify an approach to successfully mitigate this image beat pattern. The presented two-sided $K$ -band 3-D mmWave imaging system achieves system resolutions of ${\delta }\text {x} = 17.07$ mm, ${\delta }\text {y} = 4.62$ mm, and ${\delta }\text {z} = 7.26$ mm, with an accuracy of 0.8 mm in the y- and z-directions. It is shown that the system is not only capable of producing beat-pattern-free 3-D images of the products inside an optically opaque corrugated cardboard shipping box but also the two-sided approach with image beat pattern correction showing an increased image volume even if portions of the scene are occluded.

This communication proposes a new all-dielectric broadband dual-band reflectarray with a large frequency ratio using low-cost 3-D printing. In contrast to conventional reflectarrays using metallic resonant cells or dielectric slabs as phasing elements with full metal ground, the proposed design uses air as the phasing element and a stepped dielectric mirror structure as the ground. In this way, the metal ground is removed, which makes the design an all-dielectric one. Taking advantage of the dielectric mirror that only exhibits a bandgap in the predesigned band while allowing electromagnetic (EM) waves to pass through it at the frequency out of the bandgap region, a dual-band reflectarray is obtained. By properly selecting the bandgap frequency of the dielectric mirror, the dual-band frequency ratio is scalable and can be very large. Furthermore, instead of using a metallic or dielectric resonator based on resonance, air layers with linear phase response are adopted as the phasing element. Thus, the reflectarray shows broadband and stable performance over the dual-band. Compared with the state-of-the-art works using printed circuit boards (PCBs) or microfabrication, the proposed design is low cost and lightweight, and can be rapidly prototyped. For proof-of-concept, a prototype operating at $K$ -band and $V$ -band with a frequency ratio of 2.7 is printed and measured.

This article presents an ultralow power K-band frequency doubler operating under 0.4-V supply voltage. With 0-dBm input signal, the frequency doubler consumes 2.4 mW and achieves −8.4-dB conversion gain (CG). The measured saturated output power is −6 dBm at 23.6 GHz, and the 3-dB bandwidth is from 20.4 to 25.4 GHz. It exhibits up to 39-dB fundamental rejection (FR). The proposed differential frequency doubler operates at an ultralow supply voltage with ultralow power consumption in active frequency doublers.

In this paper, a switchable bandstop to allpass filter using cascaded transmission line SIW resonators is proposed. The switchable filter is performed by the switchable cascaded transmission line SIW resonators using discrete PIN diodes. Therefore, it can be used for rejecting any unwanted frequencies in the communication systems. The proposed filter design is operated in K-band and targeted for millimeter wave front end system for 5G telecommunication. Two filter designs with different orientation (design A and B) are investigated for the best performance and compact size. As a result, design B is the best by giving a maximum attenuation of 39.5 dB at 26.4 GHz with the layout size of 33×30 mm.

Polarization insensitive metamaterial absorbers (MA) are currently very attractive due to their unique absorption properties at different polarization angles. As a result, this type of absorber is widely used in sensing, imaging, energy harvesting, etc. This paper presents the design and characterization of a dual-band polarization-insensitive metamaterial absorber (MA) for K-band applications. The metamaterial absorber consists of two modified split ring resonators with an inner cross conductor to achieve a 90% absorption bandwidth of 400 MHz (21.4–21.8 GHz) and 760 MHz (23.84–24.24 GHz) at transverse electromagnetic (TEM), transverse electric (TE), and transverse magnetic (TM) mode. Polarization insensitivity of different incident angles for TE and TM mode is also investigated, which reveals a similar absorption behavior up to 90°. The metamaterial structure generates single negative (SNG) property at a lower frequency of 21.6 GHz and double negative property (DNG) at an upper frequency of 24.04 GHz. The permittivity and pressure sensor application are investigated for the proposed absorber, which shows its useability in these applications. Finally, a comparison with recent works is also performed to demonstrate the feasibility of the proposed structure for K band application, like sensor, filter, invasive clock, etc.

A new broadband circularly polarized antenna is presented for K -band application in this letter. The circularly polarized radiation is realized by orthogonal-polarized slots based on a special structure of the L-shaped waveguide cavity. To verify the proposed idea, a single element and a 2 × 4-element array are designed, fabricated, and measured. The simulations are agree well with experiments. The results show that the single element achieves the 10 dB impedance bandwidth of 27.5% (18.5–24.5 GHz) and the 3 dB axial ratio bandwidth of 7.1% (19.6–21.2 GHz), while the 2 × 4 element array achieves the 10 dB impedance bandwidth of 27.1% (18.5–24 GHz) and the 3 dB axial ratio bandwidth of 18.7% (19.3–22.6 GHz). Moreover, all-metal structure of the proposed antenna is very appropriate for tough environment applications.

An ultralow-profile circularly polarized (CP) reflectarray (RA) antenna is presented in this article, based on the variable-rotation technique for beam collimation and scanning. Starting from a conventional split-loop element, a new wideband element is designed having a single conductor layer on a single thin dielectric. The RA element, based on two coupled microstrip loops, exhibits a dual-resonant CP behavior and a stable response over a wide range of incident angles and frequencies. The wideband response is explained through eigenmode and full-wave simulations in an infinite-array environment, by examining the current distributions on the coupled loops. A high-gain 900-element offset-fed RA antenna is designed for CubeSat intersatellite links at 24.6 GHz using the proposed element. A new element rotation procedure is used to determine the required rotation angles, while eliminating phase errors in the RA aperture. The antenna prototype exhibits a 1 dB gain bandwidth of 6.8% and an axial ratio smaller than 1 dB, with the array profile of only $0.042\lambda _{0}$ at 24.6 GHz. The maximum measured antenna gain is 31.5 dBi, which corresponds to a total aperture efficiency of 58%.

A waveguide dual-polarization four-way power divider is described. It relies on a novel, broadband, and compact offset twist design, enabling an output port spacing of about $0.7\lambda _{0}$ at the lowest operating frequency, which represents an improvement by approximately a factor of 2 over previously reported solutions with similar characteristics. With a highly integrated two-probe orthomode transducers (OMTs) and ${E}$ -plane T-junctions arrangement, the proposed device provides good matching to free space in a small array configuration of open-ended waveguides. The concept is detailed through a specific implementation in the ${K}$ -band, designed to operate over the frequency range of 17.7–20.2 GHz. The numerical model of the power divider alone achieves a frequency bandwidth up to about 3 GHz with a return loss better than 22 dB. Combined with an OMT for test purposes, the designed prototype demonstrates return loss better than 19 dB over the targeted bandwidth. This concept is of interest for the design of small passive array beamforming networks in the millimeter-wave band.

This brief presents a variable-gain low-noise amplifier (VG-LNA) with a common gate (CG) cross-summing configuration, which is fabricated using a 65-nm RF CMOS process. It has a wide gain control range as well as a high input 1 dB gain compression point (IP1dB) at high-gain by introducing a split common-gate transistor (SCGT) technique. In addition, output phase compensation is achieved by adopting a tuning capacitor at the cascode node. This LNA is designed as 2-stage cascode, and the area excluding the pad is 0.2 mm2. It consumes 25.2 mW with a 1.2-V power supply. It shows a gain of 25 dB and a noise figure of 3.4 dB at 22 GHz. The measured minimum IP1dB is −27.5 dBm, and the root-mean-square phase error is 0.34° over the gain control range of 14 dB at 22 GHz.

The electron beam of a ${K}$ -band space traveling-wave tube (TWT) has been investigated in a beam measurement system in this article. The primary beam emitted from a Pierce-type electron gun is scanned by a Faraday cup probe, and the beam current density distribution and envelope are determined. The spent beam is also diagnosed with a novel retarding field energy analyzer (RFEA) by using the monopulse measurement method, and a comparison of velocity distribution between the experimental result and simulation is presented.

The microwave absorption behaviour of nano-scale cobalt-zirconium co-substituted nickel-zinc ferrites Ni0.6Zn0.4(CoZr)xFe2-2xO4 (x = 0.05, 0.10, 0.15, 0.20 and 0.25) synthesized via a sol–gel citrate precursor is reported in Ku (12.4-18 GHz) and K (18-26.5 GHz) band frequencies. The dielectric characterization of the ferrites exhibits that values of real permittivity (e′) decrease over the range of Ku band frequencies but less dispersion is found in the K band. Dielectric losses are found to be maximum in composition Ni0.6Zn0.4(CoZr)0.25Fe1.5O4. The magnetic characterization exhibits that real permeability (μ′) has a constant trend over the increasing range of frequencies but prominent peaks are observed in the spectra of imaginary permeability (μ″). Highest magnetic losses are observed for composition Ni0.6Zn0.4(CoZr)0.25Fe1.5O4 similar to dielectric losses. The reflection loss (RL) minima of −42.83 dB at 16.992 GHz and −26 dB at 18.68 GHz is found for the same composition in Ku and K band, respectively, with a matching thickness of 2 mm.

This paper presents a high efficiency K-band CMOS power amplifier (PA) in GlobalFoundries (GF) 45 nm SOI CMOS technology for 5 G applications. Compared with an ordinary two-stage PA, the PA uses a ...

Hybrid aerogels combination of dielectric loss composition and magnetic loss constituent are supposed to be the appealing microwave absorption materials due to the synergy between dielectric and magnetic constituents, lightweight feature as well as multiple scattering. Herein, hybrid graphene aerogels with decoration of 1D CoNi chains and CNTs (GA-CNT-CoNi) were fabricated via a facile freeze-drying method and followed by thermal reduction. Compared with GA and GA-CoNi aerogels, 4 wt% GA-CNT-CoNi immersed in polydimethylsiloxane matrix reveals the strongest microwave absorption properties. The optimal reflection loss (RL) value is −50.8 dB at only thickness of 1.8 mm, and the effective absorption bandwidth (EAB, RL below −10 dB) can achieve 8.5 GHz (18–26.5 GHz) covering the whole K band. High ohmic loss induced by 3D macroscopic conductive network, multiple polarization as well as eddy current loss are responsible for the boosted microwave absorption. The results demonstrate that GA-CNT-CoNi aerogel reveals the characteristics of ultra-low filler content, strong absorption, ultra-wideband, small thickness and lightweight, which is considered as a promising microwave absorbing candidate.

This letter presents the design and characterization of a Doherty power amplifier for K-band applications based on the GaAs 150-nm pseudomorphic HEMT (pHEMT) technology of Qorvo. For the output power combiner, a wideband design approach, based on embedding the output capacitance of the active devices in the combiner, is applied. A state-of-the-art bandwidth of 4 GHz is achieved: in the 21–25-GHz range, the output power is above 29.5 dBm, with an associated power added efficiency (PAE) higher than 30%. At 6-dB output back-off, the PAE is above 19% while the corresponding gain is higher than 10 dB.

A compact parabolic reflector antenna aiming at radar applications in the K‐band is presented. It is mainly composed of a thermoplastic material and using classical additive techniques (also known as 3D printing), the proposed high‐gain antenna exhibits a novel and unique form factor, particularly of interest for applications with low payload capacity, for example unmanned aerial vehicles. The antenna is composed of four parts: (i) a paraboloid shape embodied in a supporting polylactic acid (PLA) material; (ii) a metallic coating applied to the paraboloid surface of (i), to enable it with electromagnetic reflecting properties; (iii) a PLA spacer that ensures the physical separation (i.e. focal distance) between parts (i) and (iv) and, finally, (iv) a microstrip patch antenna with a reduced ground plane to reduce feed blockage. Subsequently to an overview on the theoretical formulation of parabolic reflector antennas, an antenna targeting 20 dBi and a minimum bandwidth of 500 MHz operating in the 24 GHz ISM radar band have been dimensioned, optimised in CST Microwave Studio and validated against measurements performed on a physical prototype. The simulation and experimental results are in good agreement with the prototype yielding 18.3 dBi of gain and 2.2 GHz of useful bandwidth, clearly demonstrating the potential of the proposed antenna design.

This paper presents an ultra-wideband (UWB) low-noise amplifier (LNA) with extremely flat-high-gain and low-noise figure (NF). In traditional resistive feedback topology, input matching, gain, and NF cannot be balanced. For better performance trade-offs in UWB design, a novel emitter-follower resistive feedback (EFRFB) is introduced, which utilizes a common-collector amplifier followed by a feedback resistor to flatten the gain (the ripple reduced by 2.3 dB) while alleviating the constraints between the gain and input matching. The enhanced gain without restraint by S11 is exactly required for noise reduction technology. Moreover, a peaking inductor and two resistors are adopted to improve bandwidth and output matching, respectively. The proposed LNA is implemented in a 0.18-μm SiGe BiCMOS technology and occupies 0.15 mm2 without pads. Measurements demonstrate that the LNA has a gain of 19.5 dB with ripple

By means of reflecting the output radiation from a wideband Bragg reflector, a multifrequency radiation source was experimentally implemented based on a continuous wave (CW) helical gyroresonance traveling-wave tube (gyro-TWT) with an operating frequency of about 24 GHz. Oscillation regimes were obtained with distances between the spectral component at 93–122, 193–239, 311–376, 496, 624, and 736 MHz, corresponding to excitation of various combinations of longitudinal modes. Existence of regimes with the second spectral component in intensity at the same level as the intensity at the central frequency was demonstrated, which are of significant interest for multifrequency plasma heating applications.

A series of ZnFe2O4@SiO2@PPy nanocomposites with different SiO2 contents were successfully fabricated using a combination of sol-gel and in-situ polymerization processes. Spherical ZnFe2O4 particles (mean diameter ~300 nm) were first synthesized, then coated successively with conformal layers of SiO2 and polypyrrole (PPy). The electromagnetic wave (EMW) absorption properties of the resulting ZnFe2O4@(SiO2)x@PPy nanocomposites (where x = the volume of TEOS used in the synthesis) were subsequently investigated in the K band (18–26.5 GHz) and Ka band (26.5–40 GHz). Results show that the EMW absorption properties of the nanocomposites can be precisely tuned by controlling the thickness of the SiO2. Compared with ZnFe2O4@PPy, the ZnFe2O4@(SiO2)x@PPy composites exhibited enhanced reflection losses and broader effective absorption bandwidth (EAB, reflection loss less than −10 dB). The ZnFe2O4@(SiO2)1.0@PPy nanocomposite offered the best EMW absorption performance, with a minimum reflection loss (RLmin) of −29.72 dB at 24.96 GHz (EAB of 7.0 GHz, 19.5–26.5 GHz) at 1.5 mm thickness and −36.75 dB at 38.38 GHz (EAB of 9.56 GHz, 30.44–40 GHz) at 1.0 mm thickness. The main microwave absorption mechanisms used by the ZnFe2O4@SiO2@PPy composites were magnetic losses (ZnFe2O4 nanoparticles), dielectric losses (ZnFe2O4, SiO2 and PPy) and interfacial relaxation losses (at ZnFe2O4–SiO2-PPy interfaces). Results guide the development of improved microwave absorbers in the K and Ka bands.

Bio-mass materials have been selected as one of the advanced electromagnetic (EM) functional materials due to their natural porous framework for dynamically and flexibly optimizing the EM response property. Herein, we demonstrate sulfur-doped wood-derived porous carbon EM materials (SPC) for optimizing the EM response performance via the coupling between doped heterostructures and the original 3D microchannels. The experimental results reveal that both the dielectric loss capacity and interfacial impedance matching could be increased by the sulfur-doped heterostructures. By tailoring the sulfur content, the microwave absorption (normalized RLmin) of SPC could be optimized to -15.90 dB mm-1, while the effective absorption bandwidth (EABRL≤-10 dB) could cover the K band. Moreover, the shielding effectiveness of SPC can be enhanced from 10 dB to 30 dB with the assistance of water, ascribed to the super-wettability performance. This present study provides a novel strategy to further optimize the EM response performance of wood-derived materials, and meanwhile could be widely extended to other bio-mass absorbers.

In this paper, a rectifier integrated Luneburg lens is designed at K band for wireless power transfer (WPT) applications. The lens consists of two metallic layers with a gap of 0.3 mm between them and has been made by employing the glide symmetry technique. A flare is tailored to match the outer impedance of the lens to the free space impedance. Five microstrip tapers are used at intervals of $18^{0}$ at the periphery of the lens to collect the energy from it. The rectifying circuits are co-designed and are integrated with these five tapered launchers so as to make the entire structure suitable for capturing the transmitted power from the solar power satellite wirelessly, and to convert it to the equivalent voltage. Finally, all the ports are connected with a common load for DC power combining, and the overall performance of the lens integrated rectifier as an energy harvesting system is reported in terms of its power conversion efficiency (PCE).

The design of X/K‐band shared aperture antenna (SAA) single‐linear polarized K‐band, dual‐polarized (linear/circular) X‐band 36‐elements (6×6) planar array antenna with high gain, and low cost for airborne synthetic aperture radar systems is presented. To reduce the complexity and size of the feed networks, the concept of series‐feed centre‐fed open stub array with Chebyshev amplitude distribution of −25 dB side‐lobe levels (SLL) are employed for K‐band design. Two typical frequencies, X‐band and K‐band of 9.65 and 21 GHz, are chosen (frequency ratio of 1:2.176) in this proposed SAA design on a single‐layer printed circuit board. For K‐band design, SLL can be controlled by Chebyshev distribution. The amplitude is controlled by the width of the individual patch in the linear array with left and right symmetries. A 50‐Ω microstrip line with 0.7λ spacing is used in between the patches for the ±25° scan angle requirement. The measured results are consistent with the simulations and provide a matching impedance bandwidth of 10.36/1.45% at X/K‐bands, respectively. The array also has a high aperture efficiency of more than 85%, SLL of (X/K‐bands: −18.9/−25 dB), and gain of (X/K‐bands: 24.2/17.4 dBi).

We introduce a new tunable reflectarray element for an operation frequency of 26 GHz in the k-band. It is shown that a 340∘ continuous tunning range of the reflected wave can be accomplished by using an aperture-coupled patch antenna with only one single varactor diode. The simplified design and the small needed space make it usable for k-band reflectarrays with many elements. The functionality of the reflectarray element is explained and the crucial parts are analyzed. The approach to get a full phase shift is discussed in detail. A bias-T is developed to provide the control voltage to the varactor diode without interfering with the high frequency path. The high frequency path and the DC-path are decoupled by 39 dB using a bias-T. A commercial off-the-shelf varactor diode is selected and its functionality at 26 GHz is verified. Therefore, a test printed circuit board with through, reflect, line standards is developed to de-embed the varactor diode and to evaluate it with a vector network analyzer. The reflectarray is simulated in a unit cell with plane wave excitation and periodic boundary condition using the simulation software package CST Microwave Studio™.